Many different kinds of packaged products, such as food, beverages and pharmaceuticals, can be adversely impacted through exposure to oxygen. The presence of oxygen in a package can cause oxygen contamination of the product being stored therein. The reaction of oxygen with chemicals present in foods and beverages can impact their odor and flavor. The reaction of oxygen with pharmaceuticals can impact their efficacy.
Molecular oxygen (O2) can react with a number of different compounds that are found in a number of foods and beverages. Molecular oxygen can be reduced by other molecules through the addition of electrons to form, e.g., a superoxide, a hydroxyl radical, or hydrogen peroxide. Each of these reduced forms of oxygen are very reactive and are thus likely to react with a number of products in the food and beverage industry. The reduced forms of oxygen are especially likely to react with the carbon-carbon double bonds found in almost all products with complex organic components. This reaction can cause the rapid degradation of the product. For example, the oxidated product may have an altered odor or flavor. Further, only a slight amount of oxygen is necessary to eventually cause adverse effects in food. While ambient air can have around 21% oxygen, it is desirable to have an oxygen concentration of approximately 50 parts per billion or less in the packaged environment. It is most desirable to create and maintain a packaged environment free of oxygen and its reduced forms.
In order to keep a product in a substantially oxygen-free environment, two conditions are preferable. First, the container may be filled and sealed in a manner that eliminates a substantial amount of oxygen from the interior of the container. Second, the container may maintain an environment free of oxygen.
Numerous methods have been employed to seal a container with little or no oxygen inside of it. One method is to remove oxygen from the package through the use of a vacuum or through inert gas sparging. This method is somewhat effective at removing a majority of the oxygen present in ambient air from the product during packaging. However, using this method to remove substantially all oxygen is often times commercially unfeasible because of cost or time restraints. Other methods for removing oxygen from a container have therefore been developed.
However, even when a container is initially sealed with substantially no oxygen in the container, oxygen may enter the container by, for example, migrating through the container or closure material, especially at the closure/container interface. This is especially a problem with many plastics which, in their natural state, are partially porous as to oxygen. To combat this problem, containers made of plastic have been comprised of multiple layers, including a layer that may be effective in preventing oxygen from entering the closed container, such as is seen in U.S. Pat. No. 6,601,732. However, manufacturing containers with multiple layers can be complex, time consuming, and expensive. It is therefore desirable to have a structure that has an oxygen scavenger incorporated therein, thus eliminating the need for multiple layers.